Construction World December 2021

CONSULTING ENGINEERS

DESIGNAND CONSTRUCTIONOF THE 25Mℓ REINFORCED CONCRETE EMOYENI RESERVOIR

T he des ign and construct ion of the Emoyeni Reser voi r was unique in that several aspects in both areas deviated f rom previous des igns as wel l as construct ion techniques . On the des ign s ide, hi storical methods were to have a structure wi th several movement joints to al low for the movement and shrinkage of the concrete whi le st i l l maintaining water t ightness of the structure. The cl ient (eThekwini Municipal i ty) had used thi s concept des ign for most of the exi st ing reser voi rs in and around the Durban area. The problem wi th these des igns i s that they rel ied on the construct ion of the joints and speci fical ly the water bars to be undertaken correct ly. Any errors or movement of the water bars during the concrete pours resul ts in the water t ightness being compromi sed. For thi s des ign, Knight Piésold decided on a di f ferent approach, doing away wi th the movement joints in the structure. As thi s was a ver y large concrete structure (100m x 35m x 8m) , the removal of movement joints requi red careful model l ing. Furthermore, the previously ut i l i sed tapered wal l width was changed to uni form wal ls . The model l ing of the structure showed that the uni form wal ls per formed better as a propped cant i lever wi th smal ler crack width as wel l as making the reinforcing des igns at the corners s impler and eas ier to construct . These des ign changes resul ted in a structure that was commi ss ioned wi th zero leaks and a high qual i ty of concrete. On the construct ion s ide, the structure had several chal lenges . The large structure was constructed in the heart of a high- income res ident ial suburb wi th ver y l i tt le working space and wi th i ssues such as noi se pol lut ion, dust pol lut ion and traf fic congest ion to take cogni sance of. One of the unique construct ion techniques ut i l i sed on the wal ls was to pour the 8 m high wal ls in a s ingle l i f t . Thi s was done to reduce the number of construct ion joints as wel l as to reduce the Construct ion durat ion. Normal concrete pours are not done higher than about 4 m as there i s a ri sk of aggregate separat ion during the pour as wel l as the di f ficul ty in achieving adequate vibrat ion at the base of the pour. I t should be noted that the reser voi r s i te i s in a densely populated res ident ial area. Fol lowing a stakeholder meet ing wi th the res idents in the area wherein the proposed des igns were tabled, the

res idents adjacent to the s i te di sapproved wi th the s i ze and proximi ty of the structure to the s i te boundar y. The ret iculat ion system was model led us ing Bent ley WaterCAD sof tware and the future demands introduced to the system. Fol lowing a 48-hour s imulat ion i t was determined that the reser voi r s i ze could be reduced to 25 M ℓ excluding the old 5M ℓ reser voi r. To keep the system, l ive, the reser voi r would be constructed in 2 chambers such that the old reser voi r could cont inue to operate whi le chamber 1 was being constructed. Only once chamber 1 was complete and commi ss ioned could the old reser voi r be demol i shed and chamber 2 constructed. The construct ion of Emoyeni Reser voi r had many chal lenges . The reser voi r s i te i s in the middle of a high- income res ident ial area and as such an extens ive stakeholder engagement process was undertaken leading up to the construct ion commencement . On the construct ion s ide the main chal lenges faced by the contractor was the l imi ted working space, keeping the system in operat ion throughout construct ion and fini shing wi thin the t ime durat ion. Another chal lenge that the contract faced was the COVID-19 epidemic. The s i te had to be closed for the durat ion of lockdown which delayed the construct ion by three months . Once the works started again, strict safety protocols had to be ini t iated to cont inue working safely. These also caused delays to the overal l durat ion.  The l imi ted working space and l ive exi st ing system meant that the two chambers were constructed separately.

PROJECT INFORMATION

• Company entering: Knight Piésold Consulting • Project start date: July 2019 • Project end date: February 2021 • Client: eThekwini Municipality – Department of Water and Sanitation • Main Contractor: Afrostructures • Principal Agent: Knight Piésold Consulting • Project Manager: Knight Piésold Consulting • Consulting Engineer: Knight Piésold Consulting

60 20 th Best Project Awards 2021